On topology-tuned thermoelectric properties of noble metal atomic wires

Abstract

We have carried out a systematic first principles study of thermal and thermoelectric transport properties of different noble metal (viz. Ag, Cu, Au, and Pt) atomic wires modelled in different topologies by using the Landauer-Büttiker approach in the linear response regime. Both electronic and phononic contributions are considered, with the respective transmission functions determined using the non-equilibrium Green's function approach, based upon the density functional theory and the general utility lattice program, respectively. To explore the role of topology, we have considered the linear, ladder, zigzag (ZZ), and double zigzag (DZZ) topologies for each of the four wires. Numerical results are presented for the electronic κel and phononic κph thermal conductance, thermopower S, and total figure of merit ZT. In addition, the validity of the Wiedemann-Franz law in these atomic wires has been studied. Quite generally, we find a significant dependence of these properties on the wire topology. Under ambient conditions, the valence electrons are found to be the dominant carriers of heat energy in all the wires, except for the Ag, Cu, and Au wires in the DZZ topology due to their semi-metallic nature. In relative terms, the phononic contribution is minimum (∼ 4%) for the Pt wire in linear topology, while maximum (∼ 15%) for the Cu wire in ZZ topology. However, the phonon contribution increases steadily with decreasing temperature to become as large as about 30% at T = 100 K (for Cu wire in ZZ topology). In overall, the Pt wire is found to have the maximum total thermal conductance in all topologies. S and ZT, apart from depending on topology and type of metal wire, exhibit an oscillatory behaviour as a function of chemical potential μ of electrodes. S has been found to change even its sign at characteristic μ, with a maximum value of ∼±1.5 mV/K for the Au wire in DZZ topology at μ = ∓0.15 eV. Also, ZT is found to be maximum (∼ 3) for this wire, with the presence of two pronounced peaks at μ ∼±0.6 eV, apparently located at somewhat higher μ as compared to S. An analysis of our results reveals that the change in thermoelectric properties with topology stems primarily from a change in electronic band structure and phonon spectra.